Well yes, gentoo is a good idea for performance distro, but it takes a while till you compile all the packages and configure everything, however there is also great performing distro called Archlinux
it has great and friendly community, rich wiki (there are answers for nearly all the problems you might face, also alot of how-to's) and it has package manager called "pacman" and it is simple to use. Packages there, are optimized for i686 that means this distro will perform almost as fast as a gentoo.
conclusion, you can go for gentoo, probably you would get best performing distro there is, if you are not afraid to spend some sleepless nights for it
and if you got less time, i advise to go for Archlinux.